Fuzzy routing

ABSTRACT

A system and method optimizes the information flow regarding node location across a network by controlling the propagation of this information based on distance from the node. Location servers that are near to a node receive detailed information regarding the node&#39;s location; location servers that are farther from the node receive less detailed information. In like manner, periodic updates are provided less frequently to distant location servers, and preferably also based on the velocity of a mobile node, or on a priority associated with the mobile node. The location information provided in a message addressed to a node can be minimal when the message is transmitted, and additional detail can be added to this location information by routing nodes as the message is routed closer to its destination, based on information provided by the location servers.

This application claims the benefit of U.S. Provisional PatentApplication 60/569,858, filed 11 May 2004.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to the field of communication systems, and inparticular to a network that includes mobile nodes.

The proliferation of mobile communications, from Internet capabletelephones to battlefield computers has placed substantial demand onconventional networks and routing schemes. In prior art fixed networks,it is common for the network topology to be proactively distributedamong routers, and each router uses this information to pre-computeroutes through the topology. In a “reactive” routing scheme, queries arebroadcast to find a route to a node.

The addressing scheme used to identify nodes is often designed in a wayas to improve the efficiency of path computations. For example,hierarchical addresses, such as in the Internet Protocol (IP), are usedso that paths need only be computed to destination networks and not theactual destination node. In networks with mobile nodes where noparticular neighbor relationships can be assumed a priori, commonlytermed “ad-hoc” networks, the network topology is constantly changing,and the routers cannot take advantage of pre-computed paths to routepackets to a destination node.

Geographic routing has been proposed for use in ad hoc networks. Mobilenodes determine their location via GPS or other location-determiningsystems and periodically or aperiodically broadcast “Hello” messages ina proactive scheme. Nodes within range of this broadcast update theirrouting tables with the identification of the node and its currentlocation. This updated location information is further transmittedthroughout the network. In a reactive scheme, queries are broadcast, anda mobile node responds to a query for its location.

In a geographic-routing system, the header information associated witheach message contains both the addressed node's address and itslocation. Based on the addressed node's location, receiving nodesprogressively forward the message to nodes that are closer to theaddressed node's location, until the message arrives at the addressednode.

In many conventional mobile networks, any node that is capable offorwarding messages effectively serves the function of a router. For thepurposes of this disclosure, the terms ‘node’ and ‘router’ do notnecessarily imply different components; that is, a node may performrouting functions, and a router may be a source or a destination ofmessages.

Of particular note, in an ad-hoc network, or any network with mobilenodes and particularly in networks wherein nodes include routingfunctions, when a mobile node changes location, substantial overhead isconsumed to update the network topology at each node.

In “A SCALABLE LOCATION SERVICE FOR GEOGRAPHIC AD HOC ROUTING”, byJinyang Li et al. (hereinafter Li), MIT Laboratory for Computer Science,Cambridge, Mass., Li discloses a grid-based system that addresses therouting challenges in ad-hoc/mobile networks. In Li's system, thenetwork is partitioned into a hierarchical grid, typically correspondingto a geographic grid. Location servers are distributed throughout thegrid, and are accessible to nodes that are in proximity to theseservers. Nodes may also serve a dual function of routing and locationserving, although fixed location nodes are preferred for locationserving.

Within an order-1 square, at the lowest level of the Li's hierarchy, alocation server is aware of each node currently within the square. Whena location server receives a request for the location of a node that isexternal to its order-1 square, the location server forwards the messageto a location server in an order-2 square. An order-2 square comprisesfour order-1 squares, the aforementioned order-1 square and threeadjacent order-1 squares; an order-3 square comprises 4 order-2 squares,and so on. The location request continues up the hierarchy until thehierarchy includes the addressed node. When the hierarchy level is broadenough to include the addressed node, the addressed node is ‘found’, andthe location server at this level returns the addressed node's lastreported location. Using this location, messages are routed to theaddressed node using conventional geographic routing.

To reduce the overhead associated with continuously updating each node'slocation, only one location server at each hierarchy level is used tokeep track of a node's current location. To avoid burdening a singlelocation server at each level of the hierarchy with the responsibilityof tracking all the nodes within the hierarchy, each node selects itslocation server at each level of the hierarchy substantiallyindependently of other nodes' choices of their location servers. Thus,at any level of the hierarchy, only one location server receives updatedlocation information from a given node; but, more than one locationserver at each level of the hierarchy may receive updated locationinformation from more than one node. The algorithm used by each node toselect location servers is based on the address/ID of the node, and thissame algorithm is used by the other nodes to search for the locationserver corresponding to a node's address at each level of the hierarchy.The address/ID of each node is based on a hash of the node's name, toprovide a fairly uniform distribution of unique IDs.

Although Li's solution provides an efficient means of determining anode's location, it does require the formation of a hierarchical gridsystem wherein each square at the same order of the hierarchy is unique,and non-overlapping with other squares of the same order. It alsoassumes that the current location of each node is continually and/orperiodically provided to each location server at each level of thehierarchy.

It is an objective of this invention to provide a location updating andreporting service that reduces the amount of overhead typicallyassociated with routing through a network that includes mobile nodes. Itis a further objective of this invention to provide a location updatingand reporting service that eliminates the need for a sending node toknow the precise location of a destination node before sending a messageto the destination node.

These objectives, and others, are achieved by a system and method thattends to optimize the information flow regarding node location across anetwork. Location servers that are near to a node receive detailedinformation regarding the node's location; location servers that arefarther from the node receive less detailed information. In like manner,periodic updates are provided less frequently to distant locationservers, and preferably also based on the velocity of a mobile node, oron a priority associated with the mobile node. The location informationprovided in a message addressed to a node can be minimal when themessage is transmitted, and additional detail can be added to thislocation information by routing nodes as the message is routed closer toits destination, based on information provided by the location servers.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in further detail, and by way of example,with reference to the accompanying drawings wherein:

FIG. 1 illustrates an example block diagram of a network in accordancewith this invention.

FIG. 2 illustrates an example grid-based network in accordance with thisinvention.

FIG. 3 illustrates an example flow of messages in the network of FIG. 2,in accordance with this invention.

FIG. 4 illustrates an example flow diagram for updating locationinformation associated with a node in accordance with this invention.

FIG. 5 illustrates a sample message with status information associatedwith a physical location identifier.

Throughout the drawings, the same reference numerals indicate similar orcorresponding features or functions. The drawings are included forillustrative purposes and are not intended to limit the scope of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

The invention is presented using discrete blocks to represent nodes,routers, and location servers, for ease of understanding. In a typicalembodiment of this invention, some or all of these functions may becombined within a single device. Therefore, certain terms, such as“transmit”, “receive”, and so on, are to be interpreted broadly. Forexample, when this disclosure, including the claims, states that arouter “sends” or “transmits” a request to a location server, one ofordinary skill in the art will recognize that if the router and locationserver are combined within a single device, this “sending” of therequest may be as simple as changing the state of a signal within thedevice, changing the state of a variable in a computer program, callinga particular subroutine, or any of a variety of other techniquescommonly used to communicate among hardware devices or softwareroutines. In like manner, the term “message” is also to be interpretedbroadly, to include messages of all types, including data, voice, andvideo information, signaling and control information, and so on.

FIG. 1 illustrates an example network comprising nodes 110, routers 120,and location servers 150. As illustrated, these nodes 110, routers 120,and location servers 150 may be configured to communicate using wired(solid arrow symbol) or wireless (lightning bolt symbol) communications.The nodes 110S and 110D identify a source node S and a destination nodeD, respectively. In accordance with one aspect of this invention, thenode 110S sends a message intended for node 110D to a router 120S, usingwhatever location information the node 1105 currently has regarding node110D.

If the router 120S has sufficient information regarding the currentlocation of node 110D, the router 120S forwards the message on toanother router 120C that is closer to node 110D than 120S. If the router120S does not have sufficient information regarding the current locationof node 110D to forward the message, the router 120S contacts a locationserver 150S, to request the current location of node 110D. The locationservers 150 are configured to contain sufficient information to allow arouter within its domain to forward a message toward a known node in thenetwork, as discussed further below. If the particular location server150S does not have sufficient information locally, it contacts otherlocation servers 150 to obtain this information; but in a proactiverouting network, the likelihood of having to request information fromother location servers is low.

Note that, in contrast to conventional routing schemes, includinggeographic routing schemes, neither the router 120S nor the locationserver 150S is required to provide the detailed location informationthat would be required to route the message all the way to thedestination node 110D. The router 120S and location server 150S are onlyresponsible for providing sufficient information to facilitate theforwarding of the message to another router 120 that is likely to becloser to the destination node 110D than the router 120S. That is, therouter 120S need only have an approximate, or “fuzzy”, notion of wherethe node 110D is located. As the message is routed closer to the node110D, each router 120 must also have sufficient information forcontinuing the message to a router that is closer to node 110D, and thusthe degree of approximation, or “fuzziness” is reduced as the messagegets closer to the destination node 110D.

The term “precise location” is used hereinafter to indicate locationinformation that is sufficient to reach a router 120D from which a node110D at that location can be contacted directly. The term “abstractlocation” is used hereinafter to indicate location information that isinsufficient to necessarily reach a router from which a node at thatlocation can be contacted directly. Using a postal analogy, a preciselocation corresponds to a person's street address, whereas an abstractlocation might be the person's postal/zip code, or state, or country,etc. The particular levels of abstraction and the required level ofprecision to locate a node will be dependent upon the particularnetwork, and possibly particular sections of a network. For example, ina private corporate wide-area network, the building number of a person'soffice may be sufficiently precise location information forcommunicating directly with a person, regardless of where in thebuilding the person is located. In another corporate network, the floornumber of the person's current location may be required, the buildingnumber being an abstract location. In public networks, the definition ofa precise location may be dependent upon the density of communicationtowers within an area and/or the density of, for example, “Internetcafes” within another area. In a military network, the definition of aprecise location may be dependent upon the current troop deployment, theschedule of aircraft overflights, and so on. The term “assumed location”is used hereinafter to indicate the most recently reported location of anode at a location server, and may be either a precise location or anabstract location.

In Li's system, discussed above, each of the selected location serversfor a given node is provided the precise location of the node. When arouter searches for the location of a node, the hierarchy is searcheduntil a location server associated with the node is located; once thelocation server is found, the precise location of the node is providedto the router, thereby avoiding any further searches for the node'slocation. Offsetting the efficiency provided by Li's system, however, isthe requirement that each location server must be continuously updatedwith the precise location of each of its assigned nodes. Thus, if a nodetravels from a region covered by one router to a region covered byanother router, all of the location servers associated with the nodemust be updated. Also, if the node performs this travel while themessage is in transit, and the routers of Li's system are designed toroute the message based on the once-determined precise location, thereis a likelihood that the message will arrive at the ‘prior’ routerassociated with the node, rather than the currently associated router.

In accordance with this aspect of the invention, because each locationserver 150 needs only to provide sufficient information to lead themessage closer to the destination, location servers 150 that are farfrom the destination node do not need the precise location of the node.As such, less information needs to be sent to farther location servers.

In accordance with a second aspect of this invention, because thevelocity of a mobile node is finite, the rate of updating fartherlocation servers can be substantially less than the rate of updatinglocation servers that are close to the mobile node. Either or both ofthese aspects of the invention can be incorporated into an embodiment ofthis invention to reduce the overhead traffic associated with updatingthe location of mobile nodes. Reducing the amount of informationtransmitted, and/or the frequency of transmission of the information,reduces the amount of bandwidth consumed in updating the location ofmobile nodes.

In an example embodiment of this invention, some or all of the routers120 along the path of a message between a source and destination areconfigured to review the location information contained within themessage, to determine whether the location information should beupdated. This determination can be based on one or more of a variety offactors, including, but not limited to whether the location informationin the message is sufficient to continue the routing of the messagetoward the destination, and whether the location information in themessage is recent enough to provide a reliable determination of therouting required to continue the message toward the destination. Each ofthese factors is preferably dependent upon the distance between therouter and the assumed location of the destination node. That is, arouter that is far from a destination node may rely on more abstractand/or less timely location information than a router that is in closeproximity to the assumed location. Other parameters, such as the numberof hops (transmissions between routers) since the last update, distancetraveled since the last update, previously reported velocity of thedestination node, priorities associated with the message and/or thesource or destination nodes, the current route of the message, and soon, may also, or alternatively, be used to affect the determination ofwhether the location information should be updated. In lieu of specificcriteria being used for each parameter to determine whether the locationinformation should be updated, a composite “score” based on theindividual parameters may be determined, and the determination ofwhether to update the location information can be based on this score.

Note that the criteria used to determine whether to update the locationinformation need not be limited to parameters associated with theavailable location information or the routing path. For example, ifspare resources are available at a router, the router may routinely orrandomly update its locally stored location information, in response toreceipt of a message, or in anticipation of future traffic requirements.Similarly, the choice of updating the location information may be basedon the quantity of data that is being communicated to a given node, sothat large packets, or numerous packets, addressed to the given node aremost efficiently communicated through the network. These and othercriteria and techniques for determining whether to update the locationinformation will be evident to one of ordinary skill in the art in viewof this disclosure.

When a router 120 determines that the location information in a messageshould be updated, it contacts a location server 150 to obtain theupdated information. Preferably, as discussed further below, the processused to forward location information from a node 110 to the locationservers 150 is consistent with the process used to determine whetherupdated information should be obtained, so that when a router 120requests updated information, the appropriate information is availableat the location server 150. That is, for example, if a router at acertain distance from a node is configured to request updated locationinformation whenever the information in the message is over T minutesold, the process used to forward location information from the node tothe location server that serves routers at this distance preferablyupdates the location server at least every T minutes. In this manner,the information from the location server is known to be more recent thanthe information in the message. In like manner, if the router determinesthat the location information in the message is too abstract at thisdistance from the destination node, the process used to forward locationinformation to the location server is preferably configured to provideat least a less abstract level of location information. Upon receipt ofthe updated location information, the router 120 replaces the locationinformation in the message with this updated information, and forwardsthe message to a next router 120 that is closer to the destination node,based on this updated information.

FIG. 2 illustrates an example hierarchical grid-based network inaccordance with an example embodiment of this invention. In this examplegrid, a node's location designator is a concatenation of the designatorsof each grid in the hierarchy. For example, all nodes in the largerupper-left block of the network have a location designator that beginswith AW; all nodes in the larger upper-right block have an locationdesignator that begins with EW; and so on. Within the larger block aretwelve smaller boxes, which are designated by one of the lower caseletters a-d followed by one of the lower case letters x-z. Thus, all thenodes in the upper-left smaller block within the upper-left larger blockhave location designators that begin with AWax. Within each smallerblock are nine smaller blocks, which are sequentially numbered,left-to-right, top-to-bottom by the numbers 1-9. Thus, the preciselocation of the illustrated destination node 110D in FIG. 2 is EYcy9,and the precise location of the source node 110S is BXaz7.

Note that this grid-based location system is only an example, and any ofa variety of other location-designation systems could be used. Exampleconventional location-designation systems include latitude-longitudesystems, street-city-state-country system, and so on. An unconventionallocation-designation system could be a color-coding, with largestregions being defined by the primary colors, and more precisely definedregions being defined by shades and blends of these colors; for example,a node in an “orange” region is somewhere between the centers of the redand yellow regions, and so on.

Also note that “location” and “distance” as used herein are related tolocations within a network, and need not be directly related togeographic location and/or geographic distance. Often, a networktopology comprises a mix of geographic-related locations andlogically-related locations. For example, in a corporate network, thenetwork topology may include “east-coast offices”, “west-coast offices”,and “international offices”, the international offices being reachedfrom a common router, regardless of the particular geographic locationof each office. If an employee is known to be visiting overseas offices,the abstract location designator may merely be “international offices”,regardless of whether the person is visiting offices in Japan or officesin England. In like manner, certain corporate buildings may be linkedmore directly to each other, based on the functions performed at thesebuildings, than other, perhaps less important, corporate buildings,regardless of geographic location.

FIG. 3 illustrates an example routing of a message 300 from the sourcenode 110S to the destination node D, 110D, using the example grid-basedrouting system of FIG. 2.

In this example, the source node 110S is only aware that the node D wasin the general area of E in the grid of FIG. 2, and sends the message300 with this location information 301 to the router 120S. Each router120 includes one or more receiver/transmitters 122, which may be wiredor wireless, or a combination of both, for receiving messages from nodeswithin its area, and a locator 124 that is configured to determinewhether the location information within each message needs updating, andif so, requests the information from an information server 150. In theexample of FIG. 3, the locator 124 of router 120S determines that thelocation information 301 in the message 300 needs updating, eitherbecause it is too abstract, or too old, and requests an update from thelocation server 150S. Depending upon the particular network, thisrequest may be communicated via the receiver/transmitter 122, or via adifferent receiver/transmitter system.

Each location server 150 includes a receiver/transmitter 152 forreceiving location requests from routers 120 within its area ofresponsibility, and a processor 154 that is configured to provide theassumed location of the requested node, typically via a database 158. Inthis example, the most recent information in the database 158 at theserver 150S indicates that node D is located in block EX of the grid ofFIG. 2. As detailed below, and as illustrated in FIG. 2, this locationinformation is incorrect, because node D is currently located in blockEY of FIG. 2. In this example, the server 150S is far from node D, andin accordance with one aspect of this invention, does not receivefrequent updates of node D's location. However, the information providedby the server 150S is sufficient for the router 120S to determine arouting path that will bring the message 300 closer to node D.

Upon receipt of the updated, albeit incorrect, location information fromthe server 150S, the router 120S updates the message 300 with thelocation information 302 from the server 150S and transmits the updatedmessage 300 to another router 120. The transmission process includesboth a choice of the next router 120 and the communication of themessage to the chosen next router 120. The choice of the next router 120is based on conventional routing principles, commonly known to thoseskilled in the art. In a straightforward embodiment, the router 120Sselects the next router 120 based on a distance-minimization algorithm,wherein a shortest path from server 120S to node D's location isdetermined, and the message is forwarded to the first router on thispath. Other criteria may be used in lieu of or in conjunction with, thisdistance-minimization algorithm to select among available routers, suchas the number, type, or capacity of the neighbors of each router, theavailability of location servers at each router, the freshness and/orquantity of data at a location database associated with each router, andso on.

The router 120S may also update the ‘status’ of the location information302. For example, if the system is configured to determine whether anupdate is required based on the age of the location information in eachmessage, the server 150S provides the time that the destination nodeprovided this location information, and the router 120S includes thistime in the updated location information 302 that is communicated to thenext router 120. In like manner, if the system is configured todetermine whether an update is required based on other parameters, suchas the number of hops since the last update, or the path of the messagethus far, the status of the information 302 is updated to reflect theseparameters. As would be evident to one skilled in the art, updating ofthe status of the message and/or location information at each router120, such as updating a count of hops since the last information update,can be independent of whether the location information is also updatedat the router.

A sample message 300 with the aforementioned status information isillustrated in FIG. 5.

In the example of FIG. 3, the message 300 with updated locationinformation 302 is communicated from the router 120S to a router 120C,perhaps via additional routers (not illustrated) in the path betweenrouters 120S and 120C. The router 120C determines that an update to thelocation is required, either because the location (EX) is too abstract,or the time associated with the location is too far in the past, andcontacts a location server 150C for a more current or more preciselocation. The information at the location server 150C indicates that theassumed location of node D is at block EYcy in FIG. 2, and thisinformation is communicated to the router 120C. Presumably, thisinformation is more recent and/or more precise than the information thatwas available at the router 120S via the location server 150S, becausethe router 120C and server 150C are closer to the node D.

The router 120C updates the message with this updated locationinformation 303, and optionally with the time that the node D providedthis updated location information, and forwards the message to anotherrouter 120 that is closer to node D.

When the message is received at router 120D, router 120D requests acurrent location for node D from server 150D. In this example, theserver 150D notifies router 120D that the current location of node D isblock EYcy9, which is in the service range of router 120D, and router120D forwards the message directly to node D, 110D in FIG. 3. If thereported block were not in range of router 120D, router 120D would haveforwarded the message to a router 120 that was closer to node D.

Note that the example routing of FIG. 3 did not require any locationserver 150 other than the last server 150D to have the precise locationof the node D, and even allowed for one or more of the servers 150 tohave incorrect location information. Note also that in an embodimentthat uses the age of the location information as criteria for updating,the order of abstraction need not be strict. That is, for example, thenode 110S may have had precise, but old, location information regardingnode D, and may have included it in the location information 302. But,as soon as one of the routers 120S, 120C, 120D detected that thelocation information was too old to be reliable, an updated locationwould be obtained from the corresponding server 150, and this updatedlocation, at whatever abstraction level from the server 150, wouldreplace the precise location information originally provided. In likemanner, the age-related criteria will also compensate for mis-routingsthat may be caused by a fast moving node.

It is significant to note that the abstract, or fuzzy, routing techniquepresented above can be incorporated in other conventional routingschemes. For example, the principles of this invention can beincorporated in the geographic routing system of Li, discussed above, toreduce the overhead associated with updating Li's location servers. Insuch a combined embodiment, the propagation of a node's precise locationwould be limited, by the amount of information communicated and/or bythe frequency of the location updates, or both, based on thehierarchical position of each of the selected location servers for eachnode. In a straightforward embodiment, the order-1 server may receiveeach update from the node; the order-2 server may receive every-otherupdate; the order-3 server every fourth update; and so on. In accordancewith the principles of this invention, instead of relying on thelocation information provided by the first order-j server of Li that haslocation information corresponding to a destination node, thelower-order servers are accessed as the message is propagated, to obtainmore current or more precise information as the message gets closer tothe destination. Similarly, one of ordinary skill in the art willrecognize applications of the fuzzy routing techniques of this inventionto other routing schemes, based on this disclosure. In like manner, oneof ordinary skill in the art will recognize that an embodiment of thisinvention may include the ancillary techniques of other routing schemes,such as backtracking and other techniques used to avoid ‘dead-ends’ and‘loops’.

FIG. 4 illustrates a flow diagram for processing a node's locationwithin a location server and propagating the location to other locationservers (also known as “flooding” the network with the node's location).In this invention, there are two aspects related to flooding:determining whether to update the location of a node, and determiningthe extent, or range, of the updating process. For ease of presentationand understanding, these two aspects are addressed substantiallyindependently in the flow diagram of FIG. 4, although one of ordinaryskill in the art will recognize that a joint/coincident determinationcould be used.

At 410, the new location of the node, and, optionally, the timeassociated with this new location, is received and stored at thelocation server. This information may be received at the location serverdirectly from the node, or from a neighboring router of the node, orfrom another location server. If the information is received from thenode or the currently-neighboring router, the location information willbe the precise location of the node; otherwise, it may be an abstractlocation, as discussed further below.

Preferably, nodes in the network are configured to report their locationperiodically, or upon traveling a given distance, whichever occursfirst. Other criteria for reporting a node's location may be used,including, for example, whether the node has crossed a zone boundary,the amount of traffic being received by the node, and so on. If multipleparameters are used to determine whether to update a node's location, acomposite ‘score’ may be determined based on the multiple parameters,the node's location being updated when this score exceeds a giventhreshold. The scoring and/or the threshold may be specific to each nodein a network, or applicable to all the nodes of the network, or somecombination of the two. A combination of proactive and reactivelocation-update schemes may also be used, wherein, for example, locationservers prompt for location-updates from nodes that haven't recentlyupdated their location. A random/stochastic process may also be used toroutinely trigger a location update, with or without regard to otherlocation-update criteria.

Although in a typical embodiment, the node will containlocation-determining and location-reporting capabilities, othertechniques for reporting a node's location may be used. For example, anode without location-determining capabilities may announce its presencein a region with a broadcast message. If a router receives this message,the router can define the node's location as being “within one hop of mylocation”, which sufficiently defines the nodes' “precise location” asdefined above. That is, for example, with regard to FIG. 2, a routerwithin zone EYcy9 that receives the node's “hello” message andestablishes communication with the node can report the node's preciselocation as EYcy9, because a message that is routed to EYcy9 will beforwarded directly from this router to the node. In like manner, otherlocation-determining components, such as an RF location-determiningsystem, could be used to provide the location of a node.

Having stored the latest location for the node at the location server, adetermination is made as to whether to propagate the location to otherlocation servers. At 420, the location and/or time of the previouspropagation/flooding for this node is retrieved from memory, as well asany other information, that is used to facilitate the determination, asdiscussed further below. The specific tests disclosed herein areprovided as examples, and are not intended to limit the scope of thisinvention, either inclusively or exclusively. Note also that somelocation servers in the system may be configured to execute more, fewer,or different tests than other location servers, and some servers may beconfigured to always propagate the new location to other/fartherlocation servers.

At 430, the time since the last flooding is used to determine whetherthe information at the other/farther location servers is beyond a‘staleness’ threshold. At 432, the location of the node is compared tothe previously propagated location, to determine whether the informationat the other/farther location servers is still accurate. At 434, otherparameters may be processed/compared to determine whether the newlocation needs to be propagated to the other/farther servers. Forexample, the determination may be based on a status of the particularnode, which may include a priority parameter associated with the node, adetermined velocity of the node, whether the node has crossed a zoneboundary, the amount of capacity/bandwidth the node is expected torequire, and so on. Some or all of these parameters may be specified bythe node or the router and/or determined by the first location serverthat receives the new location, and subsequently transmitted with thelocation information that is forwarded to each farther location server.Additionally, the determination may be based on parameters that are notspecific to the node, such as a current level of network trafficcongestion, a performance parameter related to prior mis-routedmessages, and so on. In general, each of the tests 430-434 are specificto each node, or at least specific to nodes at a common distance fromthe location server. That is, for example, the staleness and/or distancethresholds at 430-432 are preferably based on how far the locationserver is from the latest reported location of the node. If the locationserver is far from the node, these thresholds can be larger than thoseat location servers that are closer to the node.

Note that although the tests are illustrated as being separate andindependent, for ease of understanding, one of ordinary skill in the artwill recognize that the tests may be more complex and/or interrelated.For example, the priority of a node may determine the threshold time ordistance used in the tests of 430-432. In like manner, the tests 430-432may be serial, such that both the time and distance thresholds must beexceeded, or a combination of thresholds must be exceeded, to propagatethe new location to the other location servers.

If the tests 430-434 determine that the new location is to be propagatedto other location servers, a determination is made regarding which otherlocation servers need to be provided with updated location information,at 440. The new information may be communicated on the network thatincludes the node, or a separate location-server network may be providedfor propagating this information.

Generally, the determination at 440 of which location-servers aretargets for receiving the node's location information will be based onthe new location of the node, or the time since the location of thisnode was last reported, as well as the structure of the network used toupdate the location servers. If each location server can communicateonly with neighboring location servers, a simple time or locationthresholding may be used as a simple “all or none” determination. If, onthe other hand, the network is structured such that each location servercan communicate with every other location server, different criteriawill generally be applied to each location server, or each group oflocation servers, based generally on the distance of the locationservers from the node whose location is being propagated.

As noted above, the determination of which location servers to targetfor receiving the node's location may be integral with the time andlocation tests 430, 432, for efficiency processing. In like manner, thetests 430-434 may be configured to set one or more “flooding parameters”that control the extent, or range, of the propagation of the newlocation, based on the criteria used to determine whether or not tocommence such flooding. This flooding parameter may be as simple as a“small” or “large” flood determination, wherein small impliespropagation to only adjacent/neighboring location servers, and “large”implies propagation throughout the network. Optionally, such a floodingparameter may be a measure that further refines the extent of thepropagation, the level of abstraction of the location provided todistant servers, and so on.

Other criteria for targeting location servers to receive new locationinformation may also be used. For example, if some or all of thelocation servers are also mobile, the current location, or the amount ofmovement, of each location server will likely be a factor in determiningwhether to target that location server.

The loop 450-485 illustrates the propagation the node's location to eachof the identified/target location servers. The location that is to bepropagated to each location server is determined, at 460. As notedabove, in accordance with one aspect of this invention, the preciselocation of a node need not be propagated to location servers that arefar from the node. As such, the location that is propagated to thetarget location server may be an abstract location that is based on thelatest reported location and the distance of the node from the targetlocation server. At 470, the determined location and the time associatedwith this location are forwarded to the next-farther location servers,and at 480, this forwarded information is stored, for use in determiningwhether a subsequent location of the node needs to be reported to thislocation server.

One of ordinary skill in the art will recognize that the flow diagram ofFIG. 4 illustrates only one of any number of schemes that can be used topropagate new location information, in either precise or abstract form,to location servers of this invention. For example, as noted previously,the network of this invention will generally be defined in terms of“zones”, and the propagation of location information can be madedependent primarily upon zone-crossings. That is, in a straightforwardembodiment of this invention, the flooding can be contained by onlyreporting each zone-crossing event to the location servers in theneighboring zones. Other zone-crossing rules for minimizing the overheadassociated with flooding will be evident to those skilled in the art.Using the example location-designation scheme of FIG. 2, for example,the extent of propagation of a node's location can be based on theextent of the change of location-designation between a node's priorreported location and its newly reported location.

The foregoing merely illustrates the principles of the invention. Itwill thus be appreciated that those skilled in the art will be able todevise various arrangements which, although not explicitly described orshown herein, embody the principles of the invention and are thus withinits spirit and scope. For example, the above examples illustrate aproactive routing system, wherein updated locations are provided to thelocation servers regardless of a demand for this information. In apassive routing system, the location servers are configured to requestthe location information when prompted by a router, upon receipt of amessage; in a passive embodiment of this invention, the location serverand/or the router need only request sufficient information to allow themessage to be forwarded to a closer router, and/or the information needonly be requested if the prior location information is considered stale.Each of these determinations would preferably be based on the distanceof the destination node from the requesting router. These and othersystem configuration and optimization features will be evident to one ofordinary skill in the art in view of this disclosure, and are includedwithin the scope of the following claims.

In interpreting these claims, it should be understood that:

a) the word “comprising” does not exclude the presence of other elementsor acts than those listed in a given claim;

b) the word “a” or “an” preceding an element does not exclude thepresence of a plurality of such elements;

c) any reference signs in the claims do not limit their scope;

d) several “means” may be represented by the same item or hardware orsoftware implemented structure or function;

e) each of the disclosed elements may be comprised of hardware portions(e.g., including discrete and integrated electronic circuitry), softwareportions (e.g., computer programming), and any combination thereof;

f) hardware portions may be comprised of one or both of analog anddigital portions;

g) any of the disclosed devices or portions thereof may be combinedtogether or separated into further portions unless specifically statedotherwise;

h) no specific sequence of acts is intended to be required unlessspecifically indicated; and

i) the term “plurality of” an element includes two or more of theclaimed element, and does not imply any particular range of number ofelements; that is, a plurality of elements can be as few as twoelements.

1. A router comprising: a receiver that is configured to receive amessage having a destination ID and a destination physical locationindicator, a locator that is configured to: determine an updatedphysical location indicator corresponding to the destination ID, andupdate the destination physical location indicator in the message withthe updated physical location indicator, and a transmitter that isconfigured to transmit the message, based on the updated physicallocation indicator in the message wherein the locator is furtherconfigured to determine the updated physical location indicator andupdate the destination physical location indicator based on a status ofthe destination physical location indicator in the message, the statusbeing included in the message.
 2. The router of claim 1, wherein thestatus of the destination physical location indicator in the messageincludes: a resolution associated with the destination physical locationindicator, a time associated with the destination physical locationindicator, and a number of transmissions of the message by otherrouters.
 3. The router of claim 1, wherein the locator is furtherconfigured to update the status of the destination physical locationindicator when it updates the destination physical location indicator inthe message.
 4. The router of claim 1, wherein the router is configuredto: store the updated physical location indicator corresponding to thedestination ID, and update the destination physical location indicatorin other messages that are addressed to the destination ID with thestored updated physical location indicator.
 5. The router of claim 1,further including a location server that is configured to: receive theupdated physical location indicator corresponding to the destination ID,store the updated physical location indicator corresponding to thedestination ID, and provide the updated physical location indicator tothe locator upon request.
 6. The router of claim 5, wherein the locationserver is further configured to forward an abstract physical locationindicator corresponding to the destination ID to at least one otherlocation server.
 7. The router of claim 1, wherein the transmitter isfurther configured to transmit the message based on a route followed bythe message thus far.
 8. The router of claim 1, wherein the transmitteris further configured to transmit the message based on characteristicsassociated with one or more other routers along a path to thedestination physical location indicator.
 9. The router of claim 8,wherein the characteristics associated with each other router of the oneor more other routers include one or more of: a location of the otherrouter, neighbors of the other router, location servers associated withthe other router, and a location database associated with the otherrouter.
 10. A method of routing, comprising: receiving a message havinga destination ID and a destination physical location indicator,determining an updated physical location indicator corresponding to thedestination ID, and updating the destination physical location indicatorin the message with the updated physical location indicator, andtransmitting the message, based on the updated physical locationindicator in the message wherein determining and updating the updatedphysical location indicator is based on a status of the destinationphysical location indicator in the message, the status being included inthe message.
 11. The method of claim 10, wherein the status of thedestination physical location indicator in the message includes aresolution associated with the destination physical location indicator,a time associated with the destination physical location indicator, anda number of transmissions of the message by other routers.
 12. Themethod of claim 10, wherein updating the destination physical locationindicator in the message includes updating the status of the destinationphysical location indicator.
 13. The method of claim 10, including:storing the updated physical location indicator informationcorresponding to the destination ID, and updating the destinationphysical location indicator in other messages that are addressed to thedestination ID with the updated physical location indicator.
 14. Themethod of claim 10, including: receiving the updated physical locationindicator corresponding to the destination ID, and storing the updatedphysical location indicator corresponding to the destination ID.
 15. Themethod of claim 14, including forwarding an abstract physical locationindicator corresponding to the destination ID to a node in a network.16. The method of claim 10, wherein transmitting the message is based ona route followed by the message thus far.
 17. The method of claim 10,wherein transmitting the message is based on characteristics associatedwith one or more routers along a path to the destination physicallocation indicator.
 18. The method of claim 17, wherein thecharacteristics associated with each router of the one or more routersinclude one or more of: a location of the router, neighbors of therouter, location servers associated with the router, and a locationdatabase associated with the router.